Testing method for ascertaining the saturation value of grey cast iron



Oct. 10, 1961 R. ZIEGLER ETAL 3,003,352

TESTING METHOD FOR ASCERTAINING THE SATURATION VALUE OF GREY CAST IRON Filed Aug. 12, 1957 2 Sheets-Sheet 1 7 5 fi Q INVENTORS ROLF ZIEGLER BY RICHARD GERSTNER ATTORNEYS 1961 R. ZIEGLER EI'AL 3,003,352

TESTING METHOD FOR ASCERTAINING THE SATURATION VALUE OF GREY CAST IRON Filed Aug. 12, 1957 2 Sheets-Sheet 2 519i (M sr TESTS FOR ESTABLISHING THE GAUGING CURVE o CONTROL TESTS INVENTORS ROLF Z IE GLE R BY RICHARD GERSTNER 54AM you. 9 5% A TTORNEYS United States Patent Ofice Patented Oct. 10, 1 961 3,003,352 TESTING METHOD FOR ASCERTAINING THE SATURATION VALUE OF GREY CAST IRON Rolf Ziegler and Richard Gerstner, both of Parkstrasse 21, Leoben, Styria, Austria Filed Aug. 12, 1957, Ser. No. 677,467 3 Claims. (Cl. 73-67.5)

S l: under-eutectic alloys =1: eutectic alloys S 1: super-eutectic alloys In the case of cast iron the saturation value of the iron commonly known as the carbon equivalent is determined by the contents of carbon, silicon and phosphorus, whilst the other ingredients may be disregarded. The calculation is effected for instance according to the following formula:

It is to be ascribed to the comprehensive importance of this coefiicient that the metallurgists who have to produce a cast iron type of certain strength properties of a qualified texture formation and a certain behavior of the segregations and pipings or the like have come to prescribing the saturation value on the basis of graphs and values drawn from experiments and expediencies. Pursuant to this saturation value the analysis is calculated whereby it is indifferent within certain limits'whether this saturaton value is attained by means of high carbon contents and a low Si-percentage or vice versa. f 'f Maintaining the saturation value prescribed inthecourse of the melting process gives rise to certain difliculties as the properties OfthQIaW materials are, in general, not Y exactly known, as furthermore the material during melting is subject to certain modifications caused by carbonisation and by fire loss and the like. It is therefore indispensable to examine the product in order to see whether the saturation value prescribed has really been obtained. For this purpose it is required'to carry out a chemical analysis with reference to the elements C,Si, and P for calculation of the saturation value. This proceeding is complicated, costly and time-wasting, requiring a chemical laboratory and some time (more than half-an-hour if the usual implements are used).

The drawback of this long duration of examination is especially disagreeable in the case of the so-called preliminary test. Preliminary tests are supposed to be the tests on materials which are carried out .between the tapping of the furnace and casting itself. These samples are ana- 'tail unduly long waiting periods causing a heavy cooling down of the charge. This has led to the introduction of wedge samples whichare broken and whose fractures permit drawing a conclusion on the saturation value reached.

This proceeding of course is far precise and yields only approximate values. a p

It is therefore absolutelynecessary to develop a process which permits an exact determination of the saturation value within a very short time and which furthermore makes it possible toascertain the saturation-value without having to make use of a chemical laboratory which was hitherto necessary. I

In the case of alloys which are only composed of two constituent parts there is an unambiguous connection between the composition and the velocity of sound, so that the velocity of sound permits drawing a conclusion as to the alloys composition. However this process is not applicable to alloys containing three or four components as one single measuring value, namely the velocity of sound,

is not suflicient for determining threejor four alloy ingredi- I ents. This is the reason why in the case of grey cast iron measuring the velocity of sound' will not be sufiicient for ascertaining the contents of carbon, silicon and phos' phorus.

According to the invention there is a relation betwee the sound velocity and the saturation value calculated on e basis of the above three components, the said relation dependingon the cooling conditions selected. 1

The advantage of this process consists of the possibility in ascertaining in extraordinarily short time the saturation value which is characteristic for the properties of the cast iron, thus rendering it possible to correct and modify the composition of the cast'iron in the course of the melting process. v For the case where the cooling conditions are kept constant the propagation speed of the ultrasonic waves is exclusively dependent on the saturation value. It is therefore possible to establish a graph for a certain cooling method in which their relations are expressed. By means of this graph there is no difliculty in rapidly ascertaining the saturation value of the samples to be examined by simpy proceeding to a determination of the ultrasonic spee FIG. 1 is a graph of the relationship between the relative ultrasonic speed for grey cast iron and steel and the saturation value, the cooling conditions being constant.

FIG. 2 is a graph of the relationship between the relative ultrasonic speed for grey cast iron and steel andthe ratio of the Brinell hardness to saturation value, the cooling conditions being unknown.

A typical example for a' process of this kind is given by the following detailed test:

- Five castiron' charges' of difieren't composition have been cast at a casting temperature of about 1360 in shell moulds for obtaining plates of x x 20 The cooling conditions'were kept constant as the casting 'temof the plates.

Three plates were'cast from each charge. These plates showed the following charges:

Charge N0. Plate No C Si Mn P S S5 Avera e 0.816

2 3.03 1.30 n.b. 0.319 n.b. 0.862

Average v 0.354

3.30 1.00 n.b. 0.335 n.b. 0.912

Average 7 v 0.912

Average 7 0.995

1223 3 3.00 2.25 nib. 0.348. 11.11. 1.050

Average 1.047

1 This sample was taken into consideration not at all as the casting had been defective. N.b.=not calculated.

For determining the propagation speed of the ultrasonic waves, a. standard ultrasonic instmnnent was used. It was an instrument of the type generally used for ascertaining textural irregularities in metals. Additionally this instrument was provided with a measuring device of the 7 wall thickness, said instrument having been calibrated'according to the speed of sound in steel.

By means of the measuring device for wall thicknesses, the wall thicknesses of the sample plates were determined. However the value ascertained did not tally with the real wall thickness as the instrument is calibrated to the speed of sound in steel, and as grey cast iron has a different sound propagation speed. Hence the wall thick.- ness is designated as apparent wall thickness. At the same time the real wall thickness at the same point was determined mechanically by means I of a calipers. As results from the dependence of the speed of the time and the way in the case of uniform motions the relation of the two propagation speeds is the same as that of the wall thicknesses measured:

91 nctuul mlmh 0 ,=Sound propagation speed in cast iron Ug0=SOl1I1d propagation speed in steel The quotient dependence in respect to the saturation value. The measurements yielded the following results.

1 This sample was not taken into consideration as the casting had been defective.

FIG. 1 shows the average values for saturation and relative sound speed obtained. The dependence of the two values may, in the range investigated, be represented as a straight line'with sufficient approximation, this straight line being governed by the following equation:

spam-1.01.

In order to examine the practical usefulness of the process of the invention sample plates have again been cast out of charges of unknown composition. The saturation value of these plates was first ascertained by means of the ultrasonic instrument and then by chemical analysis. The following is a summary of the results obtained.

Saturation Saturation value value Sample No. according according Deviation to the to ultrasonic chemical instrument analysis As is shown by the above, the deviation in the samples between the saturation values determined by the ultrasonic means and by chemical analysis does never exceed the value of .01. This deviation is admissible in any case as experience has proved that the chemical analysis suffers in any case from an irregularity of plus minus .01.

The great importance of the process described consists in the fact that the determination of the saturation value after tapping the melting furnace is carried out in such a short time that the composition of the charge can be carried out before the casting. In this connection it is useful to employ shell molds for casting the preliminary samples as these masks entail the particular advantage that they can be stored for a long time and that they warrant constant cooling conditions. Besides these moulds yield castings of a smooth surface so that the samples can be subjected to the ultrasonic tests as cast and without having to grind the surface. The dimensions of the sample plates must be selected in such a manner that on the one hand the solidification of the plates takes place within the grey sphere and that on the saturation value requires 1-2 minutes. To this space of time should be added the period necessary for casting and cooling the samples which are to be fixed according to the local conditions and are to be taken into account when evolving the gauging curve.

The above described examinations refer to the case of the samples used for determining the saturation value being characterized by the same cooling conditions as the samples which were used for preparing the graph and the same pouring temperature as the known specimens.

In all the cases however in which the cooling conditions are unknown it is necessary to take into consideration a further value permitting drawing a conclusion on the cooling conditions. A value of this kind is for instance the Brinell hardness (HB) which for the same saturation value is all the higher the more rapidly the cast iron has been cooled down.

As described below all these relationships have been subjected to a detailed examination. The plates cast were not only of a different chemical composition but also of a difierent wall thickness so that the cooling conditions showed great difierences. According to the usual casting conditions moulding sand was used for the plates and the casting was eflected without drying the moulds. The pouring temperature was maintained constant. of 16 charges of ditferent composition 3 plates each were cast of a difierent thickness which had been formed in a moulding box and which were connected with each other by means of a joint pouring system. These samples were used for ascertaining the chemical composi- Out 35 1 For practically applying th methods first s: is determined in the manner described above, then the graph. according to FIG. 2 is used for ascertaining the value BB Finally, on the basis of the Brinell hardness measured the value of saturation value is calculated. However the latter calculation may be replaced by adding a suitable 'nomogram'to the graph of FIG. 2.

For checking thegraph with reference to samples made from other castings the relative ultrasonic speed was determined by means of the ultrasonic instrument and the quotient was calculated on basis of the chemical analysis and the Brinell values. measured. The results have been separately entered in FIG. 2 from which it may be gathered that they do not exceed the spreading sphere. The samples used in this connection had been made under entirely different conditions from the samples which had been used for making the graph, for instance a part of the samples have been cast in shell molds On account of the flat development of the graphand the lack of precision of the Brinell measurements this determining method is considerably less accurate than the method describedabove. I

Various embodiments of the invention may be employed within the scope of the accompanying claims.

What is claimed is:

l. A method of determining the degree of saturation of grey iron, which comprises forming by casting a plurality of grey iron test specimens of different chemical composition at a constant pouring temperature, cooling said specimens at the same rate, chemically analyzing said grey iron test specimens to determine the degree of saturation of each specimen, subjecting each of said specimens to ultrasonic impulses to determine the apparent thickness of each of said specimens, producing a graph The following table is asummary of the results: by plotting the quotients obtained by dividing the actual Wall thickness chain. analysis S8 calculatedac- Sample No. cording to 6 mm. 15 mm. 35 mm.

fol'nilla 0 Si Mn P 8 HB 91 1113 E EB &

30/5 veg 30/5 v81 30/5 091 1-- 2.81 1.17 0.57 0.070 0.034 0.73 432 11.11 420 n.b. 250 0.843 2.. 2.77 2.32 0.50 0.009 0.034 0.79 272 0.817 242 0.800 209 0.784 3.. 2.74 3.38 0.50 0.008 0.033 0.87 245 0.803 213 0.792 108 0.753 4 2.71 4.24 0.55 0.007 0.033 0.94 237 0.757 179 0.722 137 0.090 5 2.97 0.80 0.54 0.107 0.024 0.70 488 n.b. 408 n.b. 250 0.860. 5 2.94 2.04 0.53 0.100 0.023 0.82 255 0.824 221 0.770 205 0.788 7 2.90 3.27 0.52 0.104 0.023 0.91 238 0.790 194 0.754 107 0.702 8 2.87 4.40 0.52 0.102 0.023 1.01 208 0.717 101 0.005 148 0.591 9 3.13 0.70 0.51 0.109 0.027 0.79 489 11.1). 442 n.b. 287 0.807 10 3.12 1.21 0.50 0.108 0.027 0.82 280 0.845 227 0.793 214 0.707 11 3.08 2.41 0.50 0.107 0.027 0.89 248 0.775 220 0.786 203 0.744 12 3.04 3.53 0.49 0.100 0.020 0.98 234 0.753 217 0.733 180 0.085 13 3.27 0.98 0.55 0.123 0.023 0.84 482 n.b. 329 0 892 195 0.798 14 3.25 1.50 0.54 0.123 0.023 0.87 249 0.818 214 0 778 195 0.770 15 3.19 2.85 0.53 0.121 0.022 0.90 225 0.755 190 0 721 140 0.082 10 3.10 3.82 0.53 0.120 0.022 1.05 207 0.731 158 0 084 150 n.b.

N.b.=san1p1es not taken into consideration, the 6 mm. samples Nos. 1, 5, 9, 13 and the 15 mm. samples 1,

5, 9 had solidified white.

The exploitation of the measuring results has shown that the relatively simple presentation may be arrived at when plotting the values L; 2 HB against So as shown in this case the dependence is linear.

The 35 mm. sample No. 16 failed in the ultra-sound experiment.

' unknown specimen being poured at the same temperature and cooled at; the same rate as said grey iron test/specimens, said apparent thickness then being divided into the actual thickness of said unknown grey iron specimen as determined by mechanical means and the resultant quotient located on said graph to establish the corresponding saturation value of said unknown grey iron specimen.

2. A method of'determining the degree of saturation of grey iron, which comprises chemically analyzing a plurality of grey iron test specimens of different composition-Tor; the degree of saturation, subjecting each of said specimens to a hardness testing device calibrated to the Brinell hardness scale to determine the Brinell hardness of each of said specimens, subjecting each of said specimens to ultrasonic impulses to determine the apparent thickness of said specimens, producing a graph by plotting the quotient obtained by dividing the degree of saturation of each specimen into the Brinell hardness thereof against the square of the quotient obtained by dividing the actual thickness of each of said specimens of a grey iron specimen, comprising the steps of forming by casting. aplurality of, grey iron test specimens of varying chemical composition with said specimens being poured at the sametemperature; cooling said specimens at. the same rate, chemically analyzing said grey iron test specimens to determine the degree of saturation of each, subjecting each of said specimens to ultrasonic impulses to determine the apparent thickness thereof, the degree of saturation of each of said specimensthen being related to the quotient obtained by dividing the apparent thickness of each specimen into the actual thickness to establish an empirical relationship between the saturation as determined mechanically by the apparent thickness" and drawing a substantially straight line through the V plotted points, subjecting a specimen having an unknown degree of saturation to a hardness testing device calibrated to the Brinell hardness scale to determine the Brinell hardness of the specimen, and subjecting said unknown specimen to ultrasonic impulses to determine the apparent thickness of said specimen, said apparent thickness then being divided into the actual thickness of said specimen and the resultant quotient squared and located on said graph to determine the saturation value of said specimen using the previously determined Brinell hardness thereof.

value and 'the said quotient, and subjecting an unknown grey iron specimen poured at the same temperature as said test specimens and cooled at the same rate to ultrasonic impulses to determine the apparent thickness thereof, said apparent thickness then being divided into the actual thickness of the unknown specimen and the resulting quotient used in said previously established empirical relationship to determine the saturation value of said unknown specimen.

Periodical, Mesures, June 1955, pp. 427-429. (A photostat copy is in Div. 36, 73-675. 7

Hikata et al.: Sensitivity of Ultrasonic Attenuation and Velocity'Changes to Plastic Deformation and Recov- 7 cry in Aluminum, Journal of' Applied Physics, vol. 27 #4, April 1956, pp. 396-399; (Copy in 73-67.5.) 

1. A METHOD OF DETERMINING THE DEGREE OF SATURATION OF GREY IRON, WHICH COMPRISES FORMING BY CASTING A PLURALITY OF GREY IRON TEST SPECIMENS OF DIFFERENT CHEMICAL COMPOSITION AT A CONSTANT POURING TEMPERATURE, COOLING SAID SPECIMENS AT THE SAME RATE, CHEMICALLY ANALYZING SAID GREY IRON TEST SPECIMENS TO DETERMINE THE DEGREE OF SATURATION OF EACH SPECIMEN, SUBJECTING EACH OF SAID SPECIMENS TO ULTRASONIC IMPULSES TO DETERMINE THE APPARENT THICKNESS OF EACH OF SAID SPECIMENS, PRODUCING A GRAPH BY PLOTTING THE QUOTIENTS OBTAINED BY DIVIDING THE ACTUAL THICKNESS OF SAID GREY IRON TEST SPECIMENS AS DETERMINED BY MECHANICAL MEANS BY THE APPARENT THICKNESS AGAINST THE SATURATION VALUE OF SAID GREY IRON TEST SPECIMENS AND DRAWING A SUBSTANTIALLY STRAIGHT LINE THROUGH THE PLOTTED POINTS, AND SUBJECTING A GREY IRON SPECIMEN HAVING AN UNKNOWN DEGREE OF SATURATION TO ULTRASONIC IMPULSES TO DETERMINE THE APPARENT THICKNESS OF SAID SPECIMEN, SAID UNKNOWN SPECIMEN BEING POURED AT THE SAME TEMPERATURE AND COOLED AT THE SAME RATE AS SAID GREY IRON TEST SPECIMENS, SAID APPARENT THICKNESS THEN BEING DIVIDED INTO THE ACTUAL THICKNESS OF SAID UNKNOWN GREY IRON SPECIMEN AS DETERMINED BY MECHANICAL MEANS AND THE RESULTANT QUOTIENT LOCATED ON SAID GRAPH TO ESTABLISH THE CORRESPONDING SATURATION VALUE OF SAID UNKNOWN GREY IRON SPECIMEN. 